How did you install gmailwatcher? Was it a precomplied binry (.deb), through apt, or synaptic?
There are a couple of ways to remove it depending on how you installed it.
You can list all of your installed packages with
a specfic one with (substitue packageName with the actual package name)
dpkg -l | grep packageName
Then to remove it use
sudo apt-get remove packageName
Try gmail notifer. I cant guarantee its going to be the best but it looks rather promising. Here is the link to its site http://ahadiel.org/projects/gmail-notifier
Or check out CheckGmail.
Hope this info helps.